1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer or a laser beam printer, and more particularly to an image forming apparatus having a function to countermeasure an abnormal condition of a power supplied to the apparatus.
2. Description of the Prior Art
Recent image forming apparatus are controlled by digital IC's, most of which are microcomputers. In an A.C. power line voltage drops or momentarily broken during the operation of the image forming apparatus such as a recorder, the microcomputer malfunctions and the recorder is significantly influenced or a satisfactory image is not produced on a record medium or a record paper. In a worst case, the recorder is broken. In the prior art, in order to prevent such an inconvenience, means for automatically resetting the microcomputer when the voltage drop or momentary break of the power supply occurs so that the control is resumed from an initial state has been proposed. However, when the microcomputer is reset during the record operation, a setting such as the number of records changes from the initial setting and the number of records must be set again in accordance with the number of records finished and the record papers remaining in the apparatus must be removed. Such a post-processing is troublesome. When the microcomputer is reset during the record operation, all output ports are reset and the record operation is stopped. In a copying machine, for example, if the operation is stopped during the application of a predetermined latent image potential by a corona discharge to form a latent image on a photosensitive drum, an non-uniform latent image potential remains on the photosensitive drum, and in the next copying cycle, the previous copy image appears in superposition to a new copy image.
In the copying machine, the record paper under copy remains in the machine. If the record operation is stopped when the record paper is passing through a heater roller of a fixing unit and the record operation is resumed after the power has been recovered, the record paper wrapped around the heater roller is burnt, and in a worst case, a fire accident may occur.
If the microcomputer is reset when the voltage drop or the momentary break of the power occurs at a very short interval such as noise on the power line, the microcomputer is too frequently reset although the record operation is not effectively influenced by such voltage drop or momentarily break. Thus, a normal record operation cannot be continued.